Generally, a wind turbine includes a tower, a nacelle mounted on the tower, and a rotor coupled to the nacelle. The rotor generally includes a rotatable hub and a plurality of rotor blades coupled to and extending outwardly from the hub. Each rotor blade may be spaced about the hub so as to facilitate rotating the rotor to enable kinetic energy to be converted into usable mechanical energy, which may then be transmitted to an electric generator disposed within the nacelle for the production of electrical energy. Typically, a gearbox is used to drive the electric generator in response to rotation of the rotor.
The gearbox in a wind turbine is used to transform the relatively low RPM/high torque input from the rotor into a high RPM/lower torque input to the generator. Multi-stage gearboxes are generally used to achieve overall gear ratios greater than 100:1. Typically, all stages of these multi-stage gearboxes are supplied with oil from a common lubrication system wherein a pump draws oil from a sump and directs the oil through a filtration system. The oil is then cooled in a heat exchanger (cooler) to reduce the temperature of the oil to a desired gearbox oil inlet temperature. This inlet temperature is generally a compromise between the optimum oil temperatures for the various gear mesh spray and bearing components across the multiple gearbox stages. Because the optimum inlet oil temperature cannot be achieved for all of the stages, the gearing and bearing components for at least certain of the stages must be designed to compensate (e.g., oversized in some cases) for the less-than-optimum oil temperature in order to ensure the design life of the gearbox.
Accordingly, an oil temperature system and control method that provides inlet oil to the various stages of a multi-stage gearbox at temperatures set for the individual stages would be welcomed in the art.